LAM - Laboratoire d’Astrophysique de Marseille

Résumés 2016-2017

During this talk I will review past, current and future adaptive optics fed instruments at the Very Large Telescope, the challenge they represent from a science operations perspective. How do we maintain, calibrate and sometimes improve them ? What diagnostics tools and metrics are key ? How can we best prepare the 3rd generation VLT instruments and the ELT ? I will focus on NACO and SPHERE, the two instruments I supported as Instrument Scientist between 2009 and 2017. I will show some of their scientific highlights as well as original operations modes which can be game changers and open new parameter spaces, new science niches and opportunities !

30 June 2017 - 11h

Tristan Guillot (Observatoire de la Cote d’Azur)

Probing the interior of Jupiter : First results from Juno

Since July 2016, Juno is in orbit around Jupiter. Its goal is to probe the interior structure of the planet to understand its composition, dynamics, magnetic field and provide crucial constraints to understand the formation of the Solar System. I will present the results obtained after the first two perijoves, which include a deep atmosphere which is much more complex than anticipated, a more variable magnetic field and a highly accurate gravity field measurement. The latter enables the calculation of new interior models pointing to an envelope which is probably not homogeneously mixed. This has important consequences for the formation of the planet.

23 June 2017 - 11h

Mark Swinbank (Durham University)

The interaction between star formation and gas dynamics across the last 10-Gyr of cosmic time

The redshift range z=1-3 corresponds to the era when the star formation density of the Universe peaked, and the time when most of the stars in todays massive galaxies were formed. Galaxies at these early times were drastically different from those locally, with massive, gas-rich galaxies undergoing rapid star formation in globally unstable disks, and the Hubble sequence not yet in place. To understand the physical processes driving the star formation, we need to spatially resolve the star formation and gas dynamics within the inter-stellar medium (ISM) of high-redshift galaxies on scales of individual star forming regions. In this talk, I will review the latest multi-wavelength observations which aim to measure the interaction between star formation and gas dynamics within the ISM of hundreds of high-redshift galaxies on scales that range from a few kilo-parsecs to just 100’s of parsecs. The goal of the observations is to constrain how the star formation assembled the bulk of th e stellar mass in today’s massive galaxies and how secular processes crystallised the Hubble sequence around z 1.

Nebular HeII emission (at 1640 A and 4686 A in the rest-frame UV and optical ranges, respectively), observed to be more frequent in high-z galaxies than locally, is indicative of far harder ionizing spectrum than that seen in nearby systems. Star-forming galaxies with lower metal content tend to have a larger narrow (nebular) HeII intensities compared to those with higher metallicities. This agrees with the expected harder spectral energy distribution at the lower metallicities typical in the early universe. Theoretical arguments suggest that Population III stars have spectra hard enough to produce many HeII-ionizing photons. So the high-ionization HeII line has been considered one of the best signatures to single out candidates for PopIII-host galaxies and it is also a useful window into the ionizing spectrum of metal-poor hot stars. But, despite various attempts to explain the formation of nebular HeII emission, its origin remains mysterious in many cases both at high and low redshifts. Before interpreting high-z HeII emitters, it is crucial to understand HeII ionization nearby. I will discuss possible HeII-ionizing sources and what we can learn studying local, metal poor HeII-emitting galaxies by spatially resolving them.

9 June 2017 - 11h

Massimo Meneghetti (Univ. of Bologna)

Understanding strong lensing by galaxy clusters with the help of numerical simulations

Gravitational lensing is a powerful probe of the matter distribution in galaxy clusters. Understanding the inner structure of these massive systems is important for a multitude of applications : from studying the nature of dark matter, to investigating its interplay with baryons, to, more generally, understanding the process of structure formation and evolution. In addition, the magnification power of clusters as gravitational telescopes currently enables the observation of sources which would otherwise remain undetectable, at least until the advent of the next generation of space telescopes (e.g. JWST). In this talk I will use numerical and image simulations to review the methodologies employed in current lensing studies, revealing the limits and capabilities of lens modeling algorithms, and discussing how they be employed to determine several properties of galaxy clusters. In addition, if time will allow, I will discuss how simulations can be compared to state of the start lensing observations in order to test the CDM paradigm.

12 May 2017 - 11h

Pierre-Olivier Lagage (CEA-Saclay)

Characterization of the atmosphere of exoplanets with the JWST

Next year (Oct 2018), the James Webb Space Telescope will be launched. With a collecting area of 25 m², this observatory is expected to have a huge impact on many fields of astrophysics. In this talk, after having reviewed the capabilities of the JWST, shared the latest news about its status, described the timeline for forthcoming calls for science observations, I will focus on one of the main themes of the JWST : exoplanets. I will illustrate the JWST potential in the field by describing the exoplanet observations to be done in the framework of Guaranteed Time Observations (GTO). The large Signal over Noise ratio and wavelength coverage that the JWST will bring, made us studying the precision of the atmospheric models used to interpret the observation. I will present the results from benchmarking three atmospheric models. I will also show that some simplifications made so far in the models used to retrieve atmospheric parameters from observations will no longer be valid.

5 May 2017 - 11h

David Elbaz (CEA-Saclay)

Do we really know how galaxies formed their stars through cosmic time ?

There is a growing opinion among astrophysicists that we now have a clear picture about how galaxies formed their stars through cosmic time. It is thought that numerical simulations reproduce the observed Universe well enough and that we have now entered the era of the last refinements that will only validate a list of common assumptions, providing more digits in quantitative numbers measuring star formation rates, efficiencies, gas fractions, black hole masses etc.
Paradoxically, there are at the same time open questions that regularly emerge in this picture : how can a large galactic disk form and then survive a large series of merger events ? why do galaxies become passive when the vast majority of baryons remain in the form of diffuse gas in a Universe dominated by dark matter ? Dense environments segregate galaxy morphologies and yet observational evidence for an impact of the environment on the rate of star formation within galaxies remain elusive. And if we were missing a major piece of the puzzle hidden behind the so called details ? Do black holes play a role in galaxies’ history or do they just follow in parallel, and does this role inhibit or activate star formation ? I will present recent published and unpublished results obtained with Herschel and ALMA that bring some new light in this picture with peculiar emphasis on-the existence of HST-dark galaxies that may represent the missing link to understand massive galaxy formation - the ALMA view on the so-called SFR M* main sequence of galaxies - evidence for a new population of starbursts hidden within this main sequence - evidence for a paradoxical universality of galaxy growth suggesting that stellar feedback may be more a self-regulating process in galaxies than a quenching mechanism - and counter-intuitive evidence for a positive feedback of galactic black holes.

28 April 2017 - 11h

Matteo Viel (INAF Trieste)

Cosmology with the Lyman-alpha forest : new results

I will review the status of the cosmological use of the main manifestation of the intergalactic medium (i.e. the Lyman-alpha forest). After a short introduction, I will describe the use of quasar spectra at high, medium and low resolution and signal-to-noise to probe our high redshift Universe. Among the topics to be discussed I will focus on : neutrino masses, non-cold dark matter and its small scales signatures, geometrical constraints, the low redshift evolution of the forest.

7 April 2017 - 11h

Aki Roberge (NASA-GSFC)

Big Bang to Biosignatures : The LUVOIR Decadal Mission Concept

The Large UV/Optical/IR Surveyor (LUVOIR) is a concept for a highly capable, multi-wavelength observatory with ambitious science goals. This mission would enable great leaps forward in a broad range of science, from the epoch of reionization, through galaxy formation and evolution, star and planet formation, to solar system remote sensing. LUVOIR also has the major goal of characterizing habitable exoplanets around Sun-like stars and searching them for signs of life. LUVOIR is one of four Decadal Survey Mission Studies initiated in Jan 2016. The final report will be submitted to NASA and then the US National Academies in 2019. Here I will summarize LUVOIR’s broad and revolutionary science goals. I’ll explain our current vision for the instrument suite and aperture sizes to be studied. Finally, I’ll discuss the study process and what will happen over the next years in preparation for the 2020 Decadal Survey.

31 March 2017 - 11h

Edith Falgarone (LERMA)

Dissipation of turbulence in the diffuse interstellar medium and high-z starburst galaxies

Stars drive the evolution of the universe but their formation remains a theoretical challenge. One central issue in the evolution of the gas towards star formation is the dissipation of its turbulent energy at large, including the contributions of magnetic fields and cosmic-rays. A fundamental property of turbulence is its intermittency : dissipation occurs in bursts, unevenly distributed in space and time. The origin of the intermittency of turbulence is far from being understood on theoretical grounds. While it is studied in laboratory flows, its properties in compressible and non-ideal magnetized turbulence are still elusive.
Numerical simulations dedicated to turbulent dissipation in interstellar turbulence have been performed to provide observable statistical properties of intermittency. Several signatures of turbulent intermittency in the galactic interstellar medium will be presented, including those found in the all-sky polarization of the dust thermal emission of the Planck survey, and in the large abundances of some specific molecules with highly endoenergic formation routes observed with Herschel. One of these molecules has recently been discovered with the ALMA interferometer in starburst galaxies at high redshift. The absorption and emission lines unveil a hidden facet of the gravitational and turbulent energy trails in these sources.

24 March 2017 - 11h

Hèloïse Meheut (Observatoire de la Cote d’Azur)

Protoplanetary disks dynamics : from local to global approach

Protoplanetary disks are modern alchemists, they transform dust into astronomical gold : the planets ! But this is not done with the philosopher’s stone, as we know the disks have a limited life-time. To understand this life time and the conditions in which planets form, one has to study the long term dynamics of these gaseous rotating structures and explain how angular momentum is transported through or out of the disk.
After introducing the scientific context, I will present numerical simulations of protoplanetary disks showing local and global mechanisms that can be active in these disks to transport angular momentum : turbulence and outflows.

17 March 2017 - 11h

Hugues Sana (STScI)

The VLT-Flames Tarantula Survey

The VLT-Flames Tarantula Survey (VFTS) has obtained optical spectroscopy of over 800 OB and Wolf-Rayet stars in the 30 Doradus region with the aim to investigate a number of questions regarding the formation, evolution and final fate of the most massive stars and the dynamics of the region. In this presentation, I will review some of the most important results obtained by the VFTS so far, including the integrated properties of the starburst, the spin distribution and multiplicity of massive stars and the upper initial mass function.

10 March 2017 - 11h

Vardan Adibekyan (IA-Porto)

Formation and evolution of exoplanets in different environments

Shortly after the discovery of the first extra-solar planet, many studies showed that stars hosting giant planets have significant metallicity excess when compared with the stars without known giant planets. Curiously, this strong metallicity-giant planet correlation is not found for the lowest mass planets. On the other hand studies aimed to clarify whether the planet hosting stars are different from stars without planets in their content of individual elements (other than iron) yielded contradictory results. I will review the most recent results by discussing the importance of individual light and heavy elements for the formation and evolution of planets. I will also present the latest results about the role of metallicity on the architecture of planets.

3 March 2017 - 11h

Allan Sacha Brun (CEA-Saclay)

Exo-space weather

With more than 3000 exo-planetary systems discovered as of today including more than 500 planets orbiting very close (within 10 stellar radii) to their host star, it is now becoming urgent to characterize star-planet interactions for such close-in systems. Extending our knowledge of the solar system and Sun-Earth relationships to these quite different exo-systems requires to develop theoretical and numerical tools that can deal with the large diversity of stellar rotation rates, activity levels and magnetic topologies, stellar wind properties and planet’s characteristics. In this seminar I will discuss the recent progress we have made in modeling stellar magnetism, stellar wind and star-planet interactions using 3-D MHD simulations and what we have learned on the space environment surrounding exo-systems.

10 February 2017 - 11h

Thierry Foglizzo (CEA-Saclay)

The explosion mechanism of core collapse supernovae

The supernova explosion of massive stars is primarily powered by the gravitational contraction of their core into a neutron star, before the formation of a black hole. Despite numerous observations of supernovae in distant galaxies, the underlying mechanism is still a major challenge to theorists. I will review the state of the art, with an emphasis on the multidimensional effects of hydrodynamical instabilities. Numerical simulations of simplified models are used to evaluate their impact on the explosion and on the pulsar spin. Surprisingly, two of these instabilities can be illustrated with a simple hydraulic experiment based on a shallow water analogy.

The Centre for Advanced Instrumentation at Durham University, UK develops state-of-the-art instruments for application across a wide range of disciplines including astronomical instrumentation, biophysics, remote sensing and fusion diagnostics. In this talk I will focus on the KMOS multi IFU spectrograph built for the ESO VLT and the scientific results from the consortium GTO programmes.

20 January 2017 - 11h

Roger Bonnet (IAP)

Space Science in Europe

While Europe is Number one in the world in both ground-based astronomy with ESO and in nuclear physics with CERN, ESA, the largest space organization in Europe, is only Number 2 in space science. The seminar will analyze that particular situation through a brief historical review of the development of space science in Europe, followed by a reflection of why and how has Europe nevertheless been able to occupy a leading role in several areas of space astronomy, solar physics, planetary sciences and plasma physics. With a budget much bigger than ESA’s, NASA seems to have lost its capacity of reliably responding to the expectations of the US and international scientific community. The conditions of ESA’s success, based on a unique innovation approach, will be discussed in view of the future development of European Space Science and its future and essential role on the international scene.

13 January 2017 - 11h

Lia Athanassoula (Laboratoire d’Astrophysique de Marseille)

Major mergers and disc galaxy formation

Using high resolution numerical simulations — addressing the dynamics, the star formation, and the chemical evolution — we follow the formation of disc galaxies during wet major mergers in which each protogalaxy is embedded in a hot gaseous halo. We witness the destruction of the discs of the protogalaxies and the inside-out formation of a new disc, which is both massive and extended. We also witness the formation of a classical bulge component whose mass relative to the disc varies from one run to another, taking values that cover all the range from lenticulars to spiral galaxies. The rotation curves are flat. In all our simulations the disc has substructures, such as bars, lenses, spirals and rings, with realistic morphology, including ansae and boxy/peanut bulges. We will briefly discuss some dynamics of these substructures, as well as the formation and properties of the thin and thick disc components. Last but not least, we will present results on metallicity and make comparisons with observations in the bar/bulge regions of our Galaxy.

16 December 2016 - 11h

Mark Dickinson (NOAO, USA)

New views of star formation at high redshift

The history of galaxy evolution has a dirty side : much of the energy that galaxies emit over their lifetimes is absorbed and reradiated by dust. Space infrared satellites and ground-based millimeter telescopes have surveyed infrared emission from galaxies over much of cosmic history, and have demonstrated that at the peak epoch of cosmic star formation (redshift z ≈ 2), most energy from galaxies emerges in the far-infrared. But the limited angular resolution and sensitivity of most previous facilities has left us with an incomplete census : at z > 3, most of our knowledge about ordinary galaxies comes from rest-frame ultraviolet data, and we have little direct information about how much star formation at those high redshifts is obscured. Thanks to its large collecting area and high angular resolution, ALMA is now changing this story with new (sub-)millimeter data. I will discuss some new views of the dusty side of high redshift star formation from Herschel deep fields, Keck near-infrared spectroscopy, and ALMA observations.

9 December 2016 - 14h

Javier Álvarez-Márquez (Laboratoire d’Astrophysique de Marseille)

(Soutenance de thèse)

9 December 2016 - 11h

Massimo Viola (Leiden Observatory)

The Kilo Degree Survey : cosmological results

The Kilo Degree Survey (KiDS) is an ongoing ESO survey aiming at studying the growth of structures and the expansion history of the Universe using weak gravitational lensing. I will present in this talk the first constraints on cosmological parameters from a tomographic cosmic shear analysis of 450 square degree. I will discuss the level of agreement of our measurements with other cosmological probes and in particular with the Planck results as well as the implications of the measurements for cosmology.

5 December 2016 - 14h

Bruno Ribeiro (Laboratoire d’Astrophysique de Marseille)

(Soutenance de thèse)

2 December 2016 - 11h

Giuliana Fiorentino (INAF-Osservatorio Astronomico di Bologna)

Accurate Stellar Photometry in Low and Dense Environments

We will discuss the fundamental role of photometric surveys of resolved stellar populations in our Galaxy and beyond. We have recently analysed the old stellar populations, as traced by RR Lyrae stars, observed in low density environments such as the Galactic halo and dwarf galaxies surrounding the Milky Way. This investigation has revealed that small satellites can not have had a major role in building up this old component of the Galaxy, whereas the contribution of more massive dwarf galaxies like the Large Magellanic Cloud (LMC) and/or the still merging Sagittarius dwarf spheroidal galaxy can be significant. In the near future thanks to Gaia and to the Large Synoptic Survey Telescope these kind of studies will gain much more detail and will be largely extended to the the outskirts of our Local Group (distances 1Mpc).
In the next future, resolved stellar population studies need to be extended even further to explore environments still very poorly known such as the very dense core of Elliptical galaxies in Virgo or Fornax clusters (distances 18Mpc). This is very challenging and only possible exploiting the high resolution power of extremely large telescopes (40-m class). Today we need to learn how to deal with the complex modelling of the Point Spread Function across the FoV that result from the use of adaptive optics (AO) modules to assure the diffraction limit from the ground. Stars are ideal test particles to trace the performances that 1) we can reach with today 8-m class telescopes equipped with AO ; 2) we expect from the new generation of giant telescopes. We will describe a systematic study of galactic globular clusters in order to understand our current technical capabilities.

Understanding the process responsible for transforming star forming galaxies into passive and quiescent systems is currently one of the hottest topics in astronomy. I will discuss recent observational results probing different mechanisms at work in different galaxies and at different epochs. I will present multi-wavelength observations providing evidence that powerful starburst-driven and AGN-driven outflows have a profound impact on the evolution of galaxies, both locally and at high redshift, by removing huge amount of gas. However such massive outflows may not be able to completely quench star formation in galaxies and actually, in some cases, such outflows can even boost star formation. I will show that the analysis of the stellar metallicities in large samples of local galaxies reveals that “starvation” ( i.e. the lack of gas inflows) is actually responsible for quenching star formation in most galaxies (at least in intermediate/low-mass galaxies). I will discuss the possible mechanisms responsible for galaxy starvation. I will also present some recent results from the ongoing Manga-SDSSIV survey, which is delivering integral field spectroscopy for thousands of galaxies and providing precious spatially resolved information of the quenching processes on different galactic scale.

I will first summarize what we learned from HI observations using KAT-7, the precursor array of MeerKAT, the South African pathfinder for the SKA. I will then examine what we expect to be able to achieve, in the near future, with MeerKAT, MeerKAT+ FAST, SKA1 and SKA2.

4 November 2016 - 14h

Debora Pelliccia (Laboratoire d’Astrophysique de Marseille)

(Soutenance de thèse)

4 November 2016 - 11h

Tom Broadhurst (Univ. of Basque Country)

Three New Lensing Phenomena

I will describe the first detection of a Super Massive Black Hole revealed by its Einstein Ring, in Hubble Frontier Field data, and also in the same data I will show three individual stars detected at high redshift that are magnified 100,000 times as they cross the lensing caustic of a moving cluster (predicted by Jordi Miralda Escude, 1991). These events we see are modulated by microlensing, consistent with the level predicted by the intra cluster light, and thoroughly exclude cluster dark matter comprised of 30M_sun black holes suggested by Bird etal on the basis of the first LIGO event. An alternative lower mass, higher redshift lensed solution for the first LIGO detection is also presented, incidentally.

3 November 2016 - 15h (Bibliothèque)

Nicolas Peschken (Laboratoire d’Astrophysique de Marseille)

Formation et Evolution des disques galactiques (Soutenance de thèse)

28 October 2016 - 11h

Jose Groh (Univ. of Dublin)

The surprising look of massive stars before death

Stars more massive than about 8 Msun end their lives as a supernova (SN), an event of fundamental importance Universe-wide. The physical properties of massive stars before the SN event is very uncertain, both from theoretical and observational perspectives. In this talk, I will review recent efforts to couple stellar evolution and atmosphere modeling of stars in the pre-SN stage. These models are able to predict the high-resolution spectrum and broadband photometry, which can then be directly compared to the observations of core-collapse SN progenitors. I will discuss the surprising predictions of spectral types of massive stars before death. Depending on the initial mass and rotation, single star models indicate that massive stars die as red supergiants, yellow hypergiants, luminous blue variables, and Wolf-Rayet stars of the WN and WO subtypes. The presence of a close companion profoundly affects the fate of massive stars, and I will review the latest predictions of SN progenitors based on binary star evolution. I will finish by assessing the detectability of the different types of SN progenitors.

Understanding the origins of the statistical properties of stellar systems

I will present results from numerical simulations of star cluster formation, and discuss how the physical processes involved in star formation may lead to the observed properties of stellar systems and whether or not these properties may vary in different environments.

6 October 2016 - 14h

Michael Marsset (Laboratoire d’Astrophysique de Marseille)

Study of the surface composition and internal structure of the ice-rich solar system small bodies (Soutenance de thèse)

I will present how current and new facilities at the Very Large Telescope are tackling some key issues in galaxy formation and evolution. In particular I will present some new results obtained with the near-IR multi-IFU KMOS and the potential of the new multi-object spectrograph MOONS.
Finally I will put these results in the context of the forthcoming European Extremely Large Telescope. The E-ELT is now under construction and with its 39-metre primary mirror it will be the largest optical/near-IR telescope in the world. I will present an overview of the E-ELT Programme, focusing on the latest status of the telescope, its instrumentation and the scientific synergies.

23 September 2016 - 11h

Francois Rigaut (Australian National Observatory)

A short history of Adaptive Optics

In the past 30 years, Adaptive Optics (AO) has gone from a marginal and experimental technique to an enabling technology, integral to the Extremely Large Telescopes of the next decade. I will review the early AO history, the explosion of concepts of the early 2000, from both a European and North American perspective. I will also present Multi-Conjugate, Ground Layer and Extreme Adaptive Optics, as well as recent results pertaining to these advanced AO concepts. This talk is aimed at a general scientific and technical audience, no pre-requisite in adaptive optics required.

22 September 2016 - 14h

Mario Bonamigo (Laboratoire d’Astrophysique de Marseille)

Triaxial galaxy clusters (Soutenance de thèse)

16 September 2016 - 11h

Pascal Oesch (Observatoire de Genève)

Probing the Dawn of Galaxies

Thanks to the revolutionary capabilities of the Hubble Space Telescope we have made enormous progress in our exploration of galaxies across cosmic history over the last two decades. Hubble allowed us to push the observational frontier back to z 10-11, only 400 Myr after the Big Bang. To date, we have identified 1000 likely galaxies at z>6, with up to 20 credible candidates at z 9-11, one of which is even spectroscopically confirmed at z 11. These unprecedented samples allow us to directly track the build-up of galaxies in the heart of the cosmic reionization epoch, providing an increasingly more complete picture. For instance, in combination with deep data from the Spitzer Space Telescope we can now even probe the evolution of the stellar mass density over 97% of cosmic history. In this talk I will provide an overview of recent observational progress coming from very deep HST and Spitzer/IRAC observations as well as from ground-based imaging and spectroscopy to study the first generations of galaxies, and I will highlight the exciting possibilities that are just ahead of us based on several major upcoming and planned telescopes.